1. Field of the Invention
The present invention relates to an apparatus insertable on a fluid transmission conduit between a source point and a pressure responsive device to prevent over-pressurization of the pressure responsive device when pressure within the transmission conduit exceeds a predetermined value.
2. Description of the Prior Art
In order to prevent over-pressurization of pressure responsive devices, such as relay valves, safety valves, devices containing sensitive diaphragms, and the like, a relief means typically is incorporated within the pressure responsive device, or, alternatively, along the fluid pressure transmission conduit for relieving pressure in excess of a predetermined value in order to prevent damage from occuring to sensitive components in the pressure responsive device, such as elastomer seals, valve seats, and the like, as a result of exposure to pressures in excess of the tolerable operation range for the pressure responsive device. Typically, such prior art devices prevent such over-pressurization of the pressure responsive device by venting excess pressure within the pressure transmission conduit to atmosphere. Such an approach is disadvantageous because, particularly in the case of hydraulic pressure responsive devices, such venting will have a negative environmental impact.
Moreover, many prior art devices have provided a vent on the fluid pressure transmission conduit to prevent over-pressuring of the pressure responsive device by utilization of a piston or spool-like device, which either carries or receives elastomeric seals which, after repeated use, may have reduced pressure sensing integrity because of frictional wear on the seal face.
The present invention provides a method and apparatus for prevention of over-pressurization of a pressure responsive device by providing a frictionless ball valve head which is selectively shiftable to sealing engagement upon a companion seat therefor. Because of the essentially frictionless contact of the ball relative to its seat, no friction wear will result upon the outer surface of the ball element, resulting in a considerable extension of life when compared to typical elastomer sealing elements utilized on pistons and spools in prior art devices. Moreover, the present device is automatically resettable and does not require mechanical resetting subsequent to being placed in its pressure isolating mode.